(172c) Understanding Surfactant Transport of Soluble Commercial Surfactant Mixtures for Fluorine-Free Firefighting

Aqueous film-forming foams (AFFF) are critical for suppressing fuel fires, primarily due to their ability to rapidly spread and form a thin aqueous film over hydrocarbon fuels. This spreading behavior is a result of a high spreading coefficient, which is determined by surface and interfacial tensions. Traditionally, PFAS-based surfactants have been key to this performance, offering low surface tension and exceptional film stability. However, growing environmental and health concerns have led to bans on PFAS compounds, creating an urgent need for effective PFAS-free alternatives. This study examines the surfactant transport to fluid-fluid interfaces in commercial PFAS-free surfactant mixtures, known to suppress fuel fires, using pendant drop (PD) and capillary pressure microtensiometer (CPM) to measure the interface tension. Interestingly, some surfactant mixtures exhibit complex stepwise adsorption kinetics, reflecting underlying chemical heterogeneity. To interpret this behavior, a novel modeling framework is developed that accounts for multiple adsorption states. Key equilibrium properties and diffusivity for individual surfactant components are evaluated. These findings contribute to understanding the chemical composition of essential commercial surfactants, paving the way for optimized compositions of PFAS-free firefighting foam formulations.